The present disclosure relates generally to positive displacement pump systems. More particularly, the present disclosure relates to drive systems for reciprocating pumps and methods for controlling reciprocation.
Positive displacement pumps comprise systems in which a fixed volume of material is drawn into an expanding chamber and pushed out of the chamber as it contracts. Such pumps typically comprise a reciprocating pumping mechanism, such as a piston, or a rotary pumping mechanism, such as a gear set. Reciprocating piston pumps, therefore, require a bi-directional input that can drive the piston to expand and collapse the pumping chamber. Typical pumping systems are driven by a rotary input, such as a motor with a rotating output shaft. The motors are conventionally configured as air motors powered by compressed air or electric motors powered by alternating current. Rotary inputs, thus, require the uni-directional rotation of the output shaft to be converted into a reciprocating motion. This is conventionally achieved by the use of crankshaft or cam systems, such as is described in U.S. Pat. No. 5,145,339 to Lehrke et al., which is assigned to Graco Inc. Air motors are inefficient in energy consumption due to the need for a motor to drive the compressor, conversion of the compressed air into rotary motion and conversion of the rotary motion to reciprocating motion. Furthermore, air motors and the compressors that power them produce undesirable amounts of noise and can experience issues relating to icing due to the contraction and expansion of the air. Electric motors achieve energy efficiency over air motors, but still require complicated mechanical devices for converting the uni-directional rotation into bi-directional, reciprocating linear motion for the pump. There is, therefore, a need for improved drive systems for reciprocating positive displacement pumps.